1. Field of the Invention
The present invention relates to an apparatus for indicating whether the screw components, such as bolts and nuts, are fastened incompletely or completely.
2. Description of the Prior Art
Connecting work of electric conductors, assembling work of equipment, construction work, and other works are often accompanied with fastening work using bolts and nuts. In those works, bolts and nuts left unfastened due to carelessness of workers and rough work, or insufficiently fastened due to negligence for a long time after temporary fastening with bare hands may develop critical failure. In order to eliminate such failure, the following prior art has been proposed.
In the Japanese utility model publication No. 28992/1973, for example, there is disclosed a bolt assembly which has a fastener head. The fastener head has a stress concentrating portion in the axial extension (longitudinal direction) of a bolt which has been mounted on the bolt head through the stress concentrating portion in a detachable manner. When the bolt is screwed by the fastener head with a tool and attained the predetermined torque, the stress concentrating portion is destroyed to separate the fastener head. Incompleteness and completeness of fastening are indicated by whether or not the fastener head exists on the bolt head.
Also, in the Japanese utility model publication No. 44830/1976, there is disclosed a twin headed member having a stress concentrating portion formed by providing cuts from the perimeter on the middle part of the axial extension. When one head of the twin headed member is fitted in the bolt head and the bolt is rotated by the other head with a tool, the stress concentrating portion is broken at the predetermined torque.
In both structures of the prior art, however, since a head to be first rotated with a tool and a stress concentrating portion to be broken at the predetermined torque are positioned on the axial extension of the bolt, the height of the bolt head increases toward the axial extension of the bolt at least by the sum of each height of the head to be rotated with a tool and the stress concentrating portion, and as a result, space to be occupied with the bolt head increases. Consequently, in a working place where there is no space in the altitudinal direction of the bolt head, the structures of the prior art will cause such an inconvenience as impossibility of mounting bolts.
In addition, since those structures disclosed in the above-mentioned Japanese utility model publications have been invented only for application to bolts, the structures are not applicable to nuts.